The present invention relates to hydraulic apparatus in general and more particularly to a hydraulic control apparatus comprising a hydraulic master cylinder and a hydraulic slave cylinder for operating a mechanism remotely located from the master cylinder [the hydraulic control apparatus being prefilled with hydraulic fluid and pretested prior to shipment to a motor vehicle manufacturer for installation in a motor vehicle].
It is known to prefill with hydraulic fluid a motor vehicle clutch control apparatus comprising a master cylinder, a reservoir of hydraulic fluid and a slave cylinder for operating the throw out bearing of a mechanical diaphragm spring clutch. Such prefilled hydraulic control apparatus are shown, for example, in U.S. Pat. Nos. 4,407,125, 4,599,860, 4,503,678, 4,506,507, 4,959,960, and 4,993,259, all assigned to the assignee of the present invention.
As is well known, prefilling with hydraulic fluid and pretesting hydraulic apparatus for operating motor vehicle mechanisms such as mechanical clutches presents the many advantages, for the motor vehicle manufacturer, of receiving a fully assembled mechanism comprising all of the components filled with hydraulic fluid and pretested for proper operation ready to install on a motor vehicle on the assembly line without requiring that the components be installed, separately connected by way of a flexible conduit, and filled after installation with hydraulic fluid while being purged of any atmospheric air contained in the apparatus.
Fast, efficient and accurate prefilling and testing of the hydraulic apparatus is critical to the commercialization of such prefilled controlled apparatus. Various filling and testing methods are disclosed in the above-identified patents assigned to applicant's assignee.
Specifically, in U.S. Pat. No. 4,407,125, liquid is supplied through the open top of the reservoir until the liquid bleeds out of a bleed port in the slave cylinder whereupon the filling is terminated.
In U.S. Pat. Nos. 4,506,507 and 4,503,678, a port is provided in a side wall of the reservoir, vacuum is applied to the system through the port to evacuate the system, liquid is introduced into the system through the port, and the port is thereafter sealed with a plug which serves to allow flow of hydraulic fluid out of the reservoir upon excess pressure but prevents reverse flow.
In U.S. Pat. No. 4,959,960, the apparatus is filled by the use of a filling head which is fitted into the open top of the reservoir and which includes a nozzle portion having an exterior surface enclosing a volume which approximates the volume of the diaphragm so that, following filling of the apparatus, removal of the filling head, and reinsertion of the diaphragm, the apparatus is automatically placed in the totally filled condition. In U.S. Pat. No. 4,993,259, the system is closed to substantially preclude escape of hydraulic fluid from the cylinder bore through the conduit means, a predetermined force is applied to the piston to urge the piston to move in the cylinder bore, and the magnitude of the movement of the piston in the cylinder bore in response to the predetermined force is measured to determine the acceptability or unacceptability of the unit under test.
Whereas the filling and testing methods disclosed in these patents have proven to be generally satisfactory, there continues to be a need to improve the apparatus and methodology of filling and testing to provide more reliable, less expensive, and faster filling and testing.